In all fluid systems, there is a need to guard against damage associated with pressure surges. Typically, a pressure surge is generated when there is a change in the rate of flow of fluid in a closed conduit. The surge pressure can be dangerously high if the change in the rate of fluid flow in the conduit is too great. In many applications, such as pipelines and storage or loading/unloading terminals, there is a need to protect equipment and personnel from the potential damages that such pressure surges create.
Pressure surges are sometimes called "water hammer." The surge of pressure can be generated by any pipeline component that causes the fluid velocity in the conduit to change. For example, surge pressures or water hammer can be created by closing an automatic emergency shut down (ESD) device, the closure or opening of a manual or power operated valve, slamming shut of a non-return valve, or starting or stopping a pump. To protect larger fluid systems from piping component failure, the pressure surge associated with the water hammer must be relieved. In piping systems, it is especially important that a surge relief system be adaptable for a quick response time, and adaptable with respect to high flow capacity.
Surge pressures may vary in magnitude from virtually undetectable to such severity as to cause major damage to equipment and possibly loss of life. Several examples of problems caused by insufficient surge protection in fluid systems include separation of flanges, pipe fatigue, weld failure or circumferential or longitudinal over stressing of the pipe, pumps knocked out of alignment, severe damage to piping and piping supports as well as damage to specialized components such as loading arms, hoses, filters and the like due to the hydraulic shock propagated through the fluid. It is important that during interruption of steady-state operation a potentially damaging transient, i.e., a water hammer, is detected, and automatically expunged by relieving a sufficient volume of fluid from the system, thereby attenuating the transient to within acceptable limits.
Typically, protection is provided by a fixed-set-point surge relief device. A fixed-set-point surge relief system provides that when the increase in pressure reaches a specific set pressure level, a valve or valves open to relieve the excess pressure and attenuate the transient.
Alternatively, a floating-set-point surge relief system provides that when the time rate of change of pressure exceeds a pre-determined value, a valve or valves open to relieve the excess pressure and control the pressure transient. An important feature of the floating-set-point system is that it provides protection from pressure surges even though the steady-state-fluid pressure level in the pipeline may change due to varying sets of operating conditions. In such situations, a surge relief system must respond rapidly yet operate very smoothly. Such a system should respond to the increasing pressure rise, i.e., the transient pressure rise, and timely open the pressure relief mechanism. Thereafter, the system should control the rate of pressure rise, the transient, to maintain the pressure within acceptable limits. The relieved flow can be dissipated in a large storage vessel and later returned to the product line.
It is, therefore, a feature of the present invention to provide a surge relief apparatus and method which is responsive to an increasing rate of pressure change.
It is a particular feature of the present invention to provide a surge relief apparatus and method which in normal use provides control of a transient surge while allowing for varying sets of operating conditions of fluid in a conduit.
It is a feature of the present invention to provide a surge relief apparatus and method which in normal use requires no separate power source.
Another feature of the present invention is to provide a surge relief apparatus and method which accommodates high flow capacity.
Another feature of the present invention is to provide a surge relief apparatus and method which in normal use has an extremely fast response time.
Yet another feature of the present invention is to provide a surge relief apparatus and method which in normal use provides the rapid opening of a line responsive to the transient effect and the controlled closing of the line.
Another feature of the invention is the detection and control of only increasing pressure surges, thereby eliminating inadvertent opening of the surge relief system during a decreasing transient.
Yet another feature of the present invention is to provide a means for simulated testing of the surge relief system, for purposes of testing the system response to a condition which would emulate the effect of a pipeline transient.
Still another feature of the present invention is to provide a surge relief apparatus and method which is suited for use with varying types of pipeline fluids.
Another feature of the present invention is to provide a surge relief apparatus and method wherein the rate of pressure change on which the system operates can be adjusted.
Additional features and advantages of the invention will be set forth in part in the description which follows, and in part will become apparent from the description, or may be learned by practice of the invention. The features and advantages of the invention may be realized by means of the combinations and steps particularly pointed out in the appended claims.